For the Alpha Cabin, with the maximum reverberationtime being T=2.5 s and the volume being V= 6,44 m3 , equation 4 yields fc= 1 246 Hz. The AlphaCabin absorption coefficient measurements arenevertheless usually considered as valid between400 Hz and 10 000 Hz...As mentioned in [11,12] another important factor is thediffraction effect due to the finite sizes of the samples.The perimeter to surface ratio E of the sample has tobe low in order to minimize the diffraction. It is the casefor large reverberant rooms (E=1, 2 m-1for a 12 m2sample) but not for the Alpha Cabin (E=3 ,7 m-1} for a1,2 m2sample)